ABSTRACT Anger and aggression are serious and frequent complicating factors in the treatment of post-traumatic stress disorder (PTSD). A host of studies now demonstrate that interpersonal aggression and anger are: i) strongly associated with post-traumatic stress disorder (for meta-analysis, see Orth &Wieland, 2006);ii) particularly pernicious among individuals with combat-related PTSD (Novaco &Chemtob, 2002);and, iii) critical barriers to effective treatment in combat-related PTSD (Forbes et al., 2003;Forbes et al., 2008). Despite the detrimental impact that anger and aggression have on the lives of combat veterans with PTSD, and despite the barrier that anger and aggression pose to treatment and recovery, very little is understood about the neurobehavioral pathology underlying interpersonal aggression in PTSD, or the capacity of individuals with PTSD to engage in cooperative interactions more generally. The broad goal of the proposed research is to address these areas. That is, we seek to identify objective behavioral and neural metrics of aggression that contribute to impaired social interactions of individuals with combat- related PTSD. To achieve this goal, the proposed project seeks to: 7 Quantify behavioral decisions and associated neural activity during aggressive and non- aggressive interpersonal exchanges among veterans with PTSD and combat-matched control veterans. 7 Quantify behavioral decisions and associated neural activity during cooperative and non- cooperative interpersonal exchanges among veterans with PTSD and combat-matched control veterans. 7 Explore whether diagnostic differences in aggression and cooperation in PTSD are related to diminished function of neural structures associated with understanding the thoughts and intentions of social partners. The development of objective neurobehavioral measures of interpersonal difficulties associated with combat-related PTSD will facilitate early identification of veterans in need of treatment, and may aid in design and implementation of targeted therapeutic interventions. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE Anger and aggression present critical barriers to recovery and prevent healthy interpersonal relationships among veterans with PTSD. The effects of anger and aggression are devastating not only to our veterans'lives, but also to veterans'families and communities. This social impact is unambiguous. We see from media reports and epidemiology studies that veterans with PTSD show high rates of aggression, and divorce rates among combat veterans are up to 60% higher than in the general population. While research into the specific relationship between aggression and treatment outcome in PTSD is ongoing, the best evidence to date indicates that anger predicts poor treatment outcome in PTSD: the strongest predictor of treatment outcome is a veteran's fear of their own anger - that is, the implications and consequences of that anger (Forbes et al., 2008). Thus, it is the veterans who feel least able to control their own anger and aggression who are least able to benefit from current treatment protocols for PTSD. While these data are unquestionable, little progress has been made toward understanding how to identify and treat the social difficulties of veterans with PTSD. Even less is understood about the neurobehavioral mechanisms that contribute to interpersonal difficulties in PTSD. The broad goal of our proposed research is to address these areas. That is, we hope to identify objective behavioral and neural mechanisms of anger and aggression that impact the social interactions of individuals with combat-related PTSD. We believe that novel, objective, and sensitive measures of interpersonal functioning in PTSD such as that proposed here are necessary to identify veterans who may need assistance and develop personalized treatments for helping veterans maintain healthy community relationships.